類似於支付寶項目，在雙擊home鍵之後應用程序進入後台程序，然後這時候將應用程序頁面隱藏，然後顯示一樣默認圖片

 //   After didFinish addObserver  accept Notification
    [[NSNotificationCenter defaultCenter]addObserver:self selector:@selector(userDidTakeScreenshot) name:UIApplicationDidEnterBackgroundNotification object:nil];

- (void)userDidTakeScreenshot
{
    
    self.lockView = [[UIImageView alloc]initWithFrame:[UIScreen mainScreen].bounds];
    UIImage *image = [UIImage imageNamed:@"Personal_logo.jpg"];
    self.lockView.image = image;
    [self.window addSubview:self.lockView];
}

- (void)applicationDidBecomeActive:(UIApplication *)application {
    
    //  進入前台移除視圖
    
    if (self.lockView)
    {
        [self.lockView removeFromSuperview];
        self.lockView = nil;
    }
    // Restart any tasks that were paused (or not yet started) while the application was inactive. If the application was previously in the background, optionally refresh the user interface.
}